For the past six years, the California Department of Water Resources (DWR) has partnered with NASA’s Jet Propulsion Laboratory (JPL), utilizing its Airborne Snow Observatory (ASO) to accurately measure the snowpack and future water runoff. If the California Legislature passes proposed Senate Bill 487 and Gov. Gavin Newsom signs it, the ASO program will be funded for 10 years, as will the technology used to measure the entire Sierra Nevada mountain range and Trinity Alps.
“I've been measuring snow for almost 40 years in California and this, by far, is a game-changer,” Frank Gehrke, former chief snow surveyor for the DWR, told Techwire. “It's been the most exciting thing that we've seen; this is the holy grail of snow surveys.”
Airborne Snow Observatory
The ASO pilot was developed in 2013 through a partnership between NASA/JPL and the DWR, and it consists of an imaging spectrometer and scanning Light Detection and Ranging (lidar) system. NASA owns the ASO, with project funding coming from NASA Terrestrial Hydrology, NASA Applied Sciences and the DWR.
If SB 487 passes, however, funding — to the tune of $15 million per year for 10 years — would come from the state’s General Fund.
The bill would require that the DWR’s snow survey program “conduct aerial surveys of the snowpack in the Trinity Alps and Sierra Nevada Mountains, including hydrologic areas that drain or supply water to certain major reservoirs and lakes,” according to its text. The DWR would be required to collect that aerial survey data up to 10 times per year in each hydrologic area, and then summarize and make that data publicly available. On March 26, the Natural Resources and Water Committee voted to pass SB 487, and referred the bill to the Appropriations Committee, where it's set for a hearing April 22.
When it’s time to measure the snowpack, Gehrke said, DWR takes the lidar-equipped King Air airplane and follows a flight plan over the mountain range, shooting out laser pulses to detect the snowpack’s depth and density, ultimately determining how much actual water is in the snowpack. At the same time, the imaging spectrometer detects the ratio of light reflected off the snow (called albedo), which helps determine when that snow will melt.
The flight plan is likened to “mowing the grass,” as the plane goes back and forth across the mountain range taking measurements. And this overall method is quite precise, says Gehrke, who’s been part of the project from the start — and continues to be even though he retired from the DWR in December.
“We … look at the results from the Airborne Snow Observatory flights that give us a total volume of snow-water equivalent in a basin,” he said, “and we're finding that it correlates to the subsequent runoff extremely accurately.”
When the ASO takes its mid-April measurements, for instance, the volume of snow-water equivalent is essentially a guarantee that that much water will end up in the reservoir. Runoff measurements using the traditional method can be up to 60 percent off, due in part to data from a system of about 150 snow sensors that end up covered in ice during warmer winters because the snow melts and then freezes.
The reservoir may get more runoff depending on subsequent storm activity, Gehrke added, but he likened the mid-April measurement to a guaranteed minimum income.
“It allows you to make much better determinations on using that water in a beneficial manner for environmental releases, hydroelectric generation, groundwater recharge,” he said, “and avoiding that late-season kind of panic of making the high[-level] releases simply because we've got a lot more water coming in than we expected.”
The major reservoirs in California have two functions: water conservation and flood control. During the winter and early spring, Gehrke said, the flood control function dominates, and that water is released from the reservoir to make space for the potential future runoff. And improving the accuracy of snow-water equivalent measurements also allows for more balance in those dry summer months.
“Now that we have a very accurate amount of water that could come into the reservoir,” he said, “the operators can make a pretty big argument with a corps of engineers that, ‘Hey, there's X amount of snow-water equivalent above my reservoir and I've got need for that, so I don't want to make a bigger hole than necessary.’”
Benefits Beyond Water
Having such accurate data sets also can be beneficial far beyond water supply forecasting, Gehrke said.
“It gets into habitat management, fire management, vegetation analyses,” he said, adding that he and the ASO team have been utilizing the collected data to enhance the Tree Mortality Task Force's work on addressing the massive tree deaths that began in 2010, the start of a five-year drought that worsened bark beetle infestations. The most recent U.S. Forest Service data shows that at least 147 million trees have died since then.
“With the ASO data, we're able to very accurately map the locations and the severity of that problem,” Gehrke said, “and that allows the land management agencies to target resources to try to mitigate that.”
And if a fire does start, he added, the ASO’s accurate topography and vegetation management data, when you include fire modeling, can give a much better idea about where that fire will spread and how quickly.
Gehrke said the California Department of Transportation and the California Office of Emergency Services also have expressed interest given the consistently updated maps and data sets the ASO provides.
“When they go in to try and deploy resources,” he said, “it helps to have very up-to-date topography and information regarding structures that they're going to have to deal with it.”
Possible Vendor Opportunities
While the project has consisted solely of a government partnership thus far, Gehrke said that should SB 487 get signed into law, the partnership will change and vendors likely will be enlisted.
“NASA doesn't do operations, so the next step is going to be evolving [the project], and we don't know what it's gonna look like yet — but basically moving away from NASA into some other creature, if you can call it that,” he said. “And then that evolving application or development, it's going to be happening over the probably the next 18 months or so.”
Gehrke says he’s unsure of whether the DWR will release an RFP or work on solidifying a public-private partnership, but one thing is for certain: One of the critical aspects from the beginning was the turnaround time. More specifically, the turnaround time for watershed managers to receive data from the ASO flight must be approximately 24 hours.
“That around 24-hour turnaround from when the plane lands to when we have products to the cooperating agencies,” he said, referring to getting water runoff data to agencies, “that’s critical to the success.”
